High-voltage instrument transformer



Dec. 7, 1965 H. RITZ HIGH-VOLTAGE INSTRUMENT TRANSFORMER Filed Feb. 13,1962 United States Patent 3,222,590 HIGH-VOLTAGE INSTRUMENT TRANSFORMERHans Ritz, 72 Alsterkrugchaussee, Hamburg, Germany Filed Feb. 13, 1962,Ser. No. 173,048 8 Claims. (Cl. 323-48) The invention relates to ahigh-voltage instrument transformer in the form of a current transformeror a combined current and voltage transformer.

It is known to provide high-voltage instrument transformers of this typewith two or more current transformer cores through which there passes acommon primary winding. Each of the cores has a secondary winding whichforms part of a separate secondary circuit. These secondary circuits aremore especially for protective purposes and for measuring purposes.

Difficulties have been encountered in developing highvoltage instrumenttransformers of the cascade type, as opposed to the single-stage type,comprising a number of separate secondary circuit-s, which operate withsimilar reliability and measuring accuracy. If there is connected inseries with the primary winding of the lower cascade stage, whichextends through the cores of the current transformer and the secondarywindings of which are intended for the connection of the protectivecircuits and of the measuring or metering circuits, an additionalcurrent transformer system forming an upper cascade stage, of which theprimary winding is connected to the highvoltage line, it is found thatwhen one secondary circuit remains open for some time a considerablefalsification of the current values in another secondary circuit mayoccur. In addition to such deficiencies with respect to measurement,there are dangers of breakdown in such a transformer (voltage rises,glow discharge effects, oil decomposition, excess heating) due toconnection faults. If, in order to obviate these disadvantages,completely separate current transformer systems were provided in all thecascade stages, i.e., if separate cores having separate coverings ofsolid insulating material also enclosing the secondary conductors wereprovided in each instance within the housing containing the insulatingliquid, a complicated and heavy construction of the transformer withlarge overall widths would be obtained.

According to the present invention there is provided a high-voltageinstrument transformer comprising a columnlike insulating housing. Tworing cores of a current transformer system are within the housing.Secondary windings of the current transformer system are provided forthe cores. Conductors extend from the secondary windings for connectionto external circuits. A body of solid insulating material encases thetwo cores, the secondary windings and the conductors. Portions of thebody define a first passage therethrough having an opening in one of thetwo cores between its two ends. Further portions of the body define asecond passage therethrough having an opening in the other of the twocores between its two ends, so that two different primary conductors canbe passed through the body, each through one only of the two cores.Further insulating material. of a kind which is liquid at least atelevated temperatures, is around the body and substantially fills thehousing.

Fora better understanding of the invention and to show by example andnot limitation, how the same may be carried into effect, reference willnow be made to the accompanying drawings in which:

FIGURES 1 and 2 illustrate diagrammatically, and partly in section, twoembodiments of a high-voltage instrument cascade transformer;

ice

FIGURE 3 illustrates a further embodiment of a highvoltage instrumentcascade transformer; and

FIGURE 4 illustrates a portion of another embodiment:

FIGURE 5 is an enlarged section through an insulating body of thetransformers taken in a portion of the body including rings 17 and 17'.It should be noted that the same reference characters will be used forsimilar elements in each of the figures.

The illustrated high-voltage instrument transformers consist ofcomponent sets each of which forms a cascade stage 1, 2 and constitutesan independent unit sealed in air-tight fashion filled with aninsulating medium introduced in liquid form. These stages are thenmounted one above the other at the place of use. A housing or insulatingmedium container of each cascade stage 1, 2 com prises a tubular ceramicinsulator 32, 32, sealed at both ends. Insulator 31, 32 is indicated inthe drawing by chain lines.

A current transformer head 3 is provided with external connecting pins4, 5 in FIGURE 1, and with a primary conductor pin 6 extendingtransversely through the head 3 in FIGURE 2. Resilient expansion vessels7 are provided for allowing for the temperature expansion of theinsulating medium filling, which are separately provided for eachself-contained cascade stage. The cascade instrument transformersaccording to FIGURES 1 and 2 are constructed as combined instrumenttransformers (current and voltage transformers), however the inventionalso contemplates their application to simple, uncombined instrumenttransformers.

In each lower cascade stage such as cascade 2 of FIG. 1, currenttransformer systems which are completely electrically and magneticallyseparate have separate primary windings 8, 9 which are provided forprotective purposes and for measuring purposes. Primary winding 8 isabout core 10 and primary winding 9 is about core 11. Separate currenttransformer ring cores 12, 13 are also provided in each upper stage 1.In the embodiment according to FIGURE 1, the cores 12 and 13 of theupper stage 1 are energised by a common primary Winding 14. The ends ofthe primary winding 14 are connected to external connecting pins 4, 5.Each current transformer core 12, 13 in each cascade stage carries asecondary winding. Core 12 has a secondary winding 40a, and core 13 hasa secondary winding 40b. Core 10 has a secondary winding 41a and core 11a secondary winding 41b. The cores 10 and 11, the winding 41 and theconductors are shown in dotted lines to indicate they are embedded ininsulation.

The current transformer ring cores 12 and 13 for protective purposes andfor measuring purposes which are disposed within each cascade stage, aswell as their secondary windings and their connecting conductors, have acommon insulating covering 15, as seen in FIGURES 1 and 2 consisting ofa material of high mechanical and dielectric strength (oil paperwrapping or cast resin covering). Conductive coatings or inserts 18, 18(FIG. 5) are provided in the covering 15 to serve for voltage control.In the current transformer system of the lower cascade stage of FIGURE 1and all the current transformer systems of the remaining figures, thering cores 10 and 11 are so arranged and enclosed by the insulatingcovering 15 that the core passages 33 and 34 are each separatelyaccessible through separate apertures 35 and 36 in the common insulatingcovering body 15 for the purpose of passing therethrough the leads 37and 3'8 of primary windings 8 and 9 respectively. The passage andapertures are best seen in FIG. 4. There are provided in each currenttransformer system two ring cores which in FIGURES 2 and 3 are disposedone above the other in each instance, the two ring cores being disposedin one plane in FIGURE 2, and in separate, parallel planes in FIGURE 3,while in FIGURE 4 they are juxtaposed in an inclined position.

The conductive inserts 18, 18' (FIGURE 5) which are provided within theinsulating covering body 15 of each current transformer system are foilshaped and completely surround the cores and 11, the secondary windings8 and 9 wound thereon together with the lead-in conductors 19c and 19dtherefore, in the manner of onion skins. They terminate in rings, 17distributed along the leadout ends (winding lobes). Rings 17 are alsocovered by material of high dielectric strength. Thus, only a fewconductive inserts are necessary for the voltage control even with highvoltages. The conductive inserts 18,18 are connected to rings 17, 17',of body 15. Inserts 18, 18' provide a uniform distribution of voltagewithin the insulating body 15. Each point of such an insert assumesautomatically the same potential or voltage, and the potential of aninner insert 18 will be greater than that of an outer insert 18. In theinsulating material between the inserts and outside thereof each pointassumes a higher or lower corresponding potential so that there areequipotential surfaces whose shape conforms or adapts to the shape ofthe inserts 13, 18 and the rings 17, '17. Sharp edges at the ends of theinserts 13, 18 are avoided by the rings 17, 17 which are covered byinsulating material 15, so that no arcing can arise there in Aconsequence of high electrical voltage. The insulating medium fillingthe column-like insulating vessel of each individual cascade stage maybe a high-grade liquid insulating medium. Alternatively, a cast resinfilling may be provided.

A voltage transformer part 20 having an iron core 21 with secondarywindings for protective and measuring or metering purposes, may also beprovided within each cascade stage. Instead of this arrangement, theremay be provided in each of the cascade stages 1, 2 a voltage transformercore provided with a secondary winding, for protective purposes and asimilar core for measuring or metering purposes.

In the instrument transformer shown in FIGURE 2, iron cores 22, 23having a closed magnetic circuit are arranged as short-circuitdissipators on the primary-conductor or connecting pin 6 or pinsextending entirely through the head 3 of the instrument transformer.Each of these cores 22 and 23 forms in combination with pin 6 a barchoke having a relatively high impedance with normal primary currentpassing through the primary conductor, so that the current flows to thecurrent transformer primary windings 24, 25. For high primary currentsor short-circuits, the impedance of the bar chokes decreases to such anextent, due to the saturation of the iron of the chokes, that thecurrent flows primarily directly through the primary conductor pin 6 andnot through the windings 24 and 25 and cannot damage the primaryWindings of the current transformer. In some cases, the primary windingof the current transformer may be connected to the pin in accordancewith the principles of an auto-transformer.

In order that the branch currents from both sides of each of the barchokes may be separately fed to the current transformer systems, i.e. inorder that the current transformer cores of the uppermost cascade stagewhich carry the low voltage may be separately provided with primarywindings carrying high voltage, the iron cores separately provided forprotective purposes and for measuring or metering purposes in the uppercascade stage in the transformer shown in FIGURE 2, as well as those inthe lower cascade stages in the current transformer systems illustratedin FIGURES 1, 2 and 3, are so arranged that separate primary windingsmay be passed through their core passages. In this case, the two cores,

including their secondary windings, which carry low voltage, arecommonly enclosed by oil paper wrappings or cast resin layers andconductive inserts disposed one within the other in the manner of onionskins, so that apertures remain free in the core apertures for thepassage therethrough of the respective primary windings carrying highvoltage.

In the arrangement according to FIGURE 2, there are provided in thelowermost current transformer cascade stage supplementaryauto-transformers 26, 27 for voltage limiting in the event of thesecondary circuit being opened.

I claim:

1. A transformer adapted to be coupled to conductors of a single phaseelectrical system comprising a hollow insulating housing, two ring-likecores in said housing each having a central opening, said cores beingdisposed adjacent one another in the same plane, separate secondarywindings each around one of said cores, conductors extending from saidseparate secondary windings and adapted to be connected to electricalcircuits, a common body of rigid insulating material encasing both saidcores, said secondary windings and portions of said conductors, saidbody having a first aperture located within the opening of one of saidring-like cores, said body having a second aperture located within theopening of the other of said ring-like cores, a first primary windingpassing through said first aperture and a second primary winding passingthrough said second aperture, said first and second primary windingsbeing adapted for connection to conductors of a single phase electricalsystem, and a liquid insulator filling said housing and encasing saidbody and said primary windings.

2. The transformer according to claim 1 further comprising spacedconductive foil shaped inserts each enclosing both said cores and saidconductors in said body for controlling the potential distributiontherein, conductive rings connected to said conductive inserts, saidrings being disposed along the said body and solid insulating materialcovering said rings to control the potential distribution in theenvironment of and along said body.

3. The transformer according to claim 1, wherein said 1ring-like coresare juxtaposed at substantially the same evel.

4. The transformer according to claim 1, wherein said ring-like coresare disposed in parallel planes.

5. The transformer of claim 1 further including a resilient expansionchamber operatively connected to said housing.

6. The transformer of claim 1 further including a second transformercomprising first and second separate transformer cores, first and secondseparate secondary wlndings each about one of said transformer cores, aninput primary winding adapted to be connected to the conductors of saidsingle phase electrical system, means for connecting said first separatesecondary winding to said first primary Winding, and means forconnecting said second separate secondary winding to said second primarywinding.

7. The transformer of claim 1 further including a second transformercomprising first and second separate transformer cores, first and secondseparate secondary windings each about one of said separate trans-formercores, means for connecting said first separate secondary winding tosaid first primary winding, means for connecting said second separatesecondary winding to said second primary winding, first and second inputprimary windings each about one of said separate transformer cores, afirst saturabl choke connected in parallel with said first input primarywinding, a second saturable choke connected in parallel with said secondinput primary winding, and means adapted for connecting said first andsecond input primary windings to the conductors of a single phaseelectrical system.

S. The transformer of claim 1 further including first 5 6 and secondauto-transformers respectively connected to 2,804,577 8/1957 Roth336-174 X said first and sec-0nd separate secondary windings. 3,024,4343/ 1962 Carson 336-174 References Cited by the Examiner FOREIGN PATENTSUNITED STATES PATENTS 5 244,927 6/1947 Switzerland.

1,790,981 2/1931 Fischer 33694 X 2,113,421 4/1938 Camill-i et a1. 336-94x JOHN BURNS Prlmary Exammer- 2,312,073 2/ 1943 Camilli 33694 E. JAMESSAX, Examiner.

1. A TRANSFORMER ADAPTED TO BE COUPLED TO CONDUCTORS OF A SINGLE PHASE ELECTRICAL SYSTEM COMPRISING A HOLLOW INSULATING HOUSING, TWO RING-LIKE CORES IN SAID HOUSING EACH HAVING A CENTRAL OPENING, SAID CORES BEING DISPOSED ADJACENT ONE ANOTHER IN THE SAME PLANE, SEPARATE SECONDARY WINDINGS EACH AROUND ONE OF SAID CORES, CONDUCTORS EXTENDING FROM SAID SEPARATE SECONDARY WINDINGS AND ADAPTED TO BE CONNECTED TO ELECTRICAL CIRCUITS, A COMMON BODY OF RIGID INSULATING MATERIAL ENCASING BOTH SAID CORES, SAID SECONDARY WINDINGS AND PORTIONS OF SAID CONDUCTORS, SAID BODY HAVING A FIRST APERTURE LOCATED WITHIN THE OPENING OF ONE OF SAID RING-LIKE CORES, SAID BODY HAVING A SECOND APERTURE LOCATED WITHIN THE OPENING OF THE OTHER OF SAID RING-LIKE CORES, A FIRST PRIMARY WINDING PASSING THROUGH SAID FIRST APERTURE AND A SECOND PRIMARY WINDING PASSING THROUGH SAID SECOND APERTURE, SAID FIRST AND SECOND PRIMARY WINDINGS BEING ADAPTED FOR CONNECTION TO CONDUCTORS OF A SINGLE PHASE ELECTRICAL SYSTEM, AND A LIQUID INSULATOR FILLING SAID HOUSING AND ENCASING SAID BODY AND SAID PRIMARY WINDINGS. 